I can't believe you're charging more than double for almost the same repairing time and parts!
「修理時間も使う部品も大差ないのに倍以上の価格設定かよ」はこのようにも言えます:
I can't believe you're charging more than double for almost the same repairing time and parts!
charge = 請求する
more than double = 倍以上 (二倍以上という直訳)
almost the same = ほとんど同じ
repairing time = 修理時間
parts = 部品
この場合には、I can't believe (that)~「~を信じられない」という表現を使えます。
There's not much difference in the parts and time required to repair newer phones compared to older phones, but they charge more than twice as much to fix newer phones.
この場合、次のような言い方ができますよ。
ーThere's not much difference in the parts and time required to repair newer phones compared to older phones, but they charge more than twice as much to fix newer phones.
「古いスマホと比べて、新しいスマホの修理に必要な部品や時間に大差はないが、新しいスマホを修理するのに倍以上請求される」There's not much difference in ... で「…に大差はない」
the parts and time required to repair で「修理に必要な部品と時間」
ご参考まで!